1. Field of the Invention
The present invention deals with the field of cosmetic preparations for improving the appearance of the human skin and, more particularly, with topical formulations for ameliorating skin lesions such as keratoses (rough exfoliating skin due to photodamage, etc.),as well as lesions showing weakened collagen fibers such as striae distensae (stretch marks).
2. Description of Related Art
Keratoses are extremely common skin lesions comprising regions of scaly, exfoliating skin caused either by sun damage (actinic keratoses) or by simple aging of the skin (nonactinic or senile keratoses). These areas of damaged skin can be surgically removed or chemically destroyed. Either of these treatments can be painful and scarring. These lesions yield, to some extent, to various topical applications of various moisturizing cosmetic substances. There has also been some success in treating these lesions with retinoic acid (see U.S. Pat. No. 3,920,835 to Van Scott et al.) and .alpha. hydroxy-fatty acids (see U.S. Pat. No. 4,234,599 to Van Scott et al.).
Stretch marks or striae distensae are common blemishes on human skin that usually are even more recalcitrant to treatment than keratoses. Stretch marks are most prevalent on females appearing in the form of white lines or "zebra stripes" and are a rather frequent complication of pregnancy. As the name suggests, the marks are commonly believed to result from the excessive stretching of the skin caused by rapid weight gain, although changes in the levels of various glucocortical hormones have also been implicated.
Normally, the skin is elastic and pliable and can adjust to increases in body girth. However, when the changes are too rapid, the skin's ability to adjust may be overwhelmed. Histologically stretch marks seem to represent a region of skin with absent or disorganized collagen bundles. Although some of the pregnancy-induced marks diminish or even disappear after pregnancy, the more severe marks are usually permanent.
Stretch marks are also formed during the adolescent growth spurt being found on adolescent males as well as females. Significant changes in weight or body size as with body builders can also induce stretch marks. There has been a considerable effort to provide preparations that either prevent the occurrence of the marks and/or promote their healing. Conventional folk wisdom has suggested that applications of various creams or emollients may have the desired effect, but there is considerable clinical controversy surrounding claims that creams and the like can have any significant effect on stretch marks.
A recent study (Madlon-Kay, D. J., Archives of Family Medicine, 2: 507-11 (1993)) found that application of various creams and oils to the skin of pregnant women had no effect on the formation of stretch marks. However, another recent study (Wierranq, F.; Kozak, W.; Schramm, W.; and Grunberger, W.; Wiener Klinische Wochenschrift, 104: 42-44 (1992)) compared a control group of 26 pregnant women with a treatment group of 24 pregnant women who were treated with applications of water/oil massage cream. This study found that whereas two-thirds of the control group developed stretch marks, only one-third of the treatment group did so. It is not clear whether the massage given in applying the preparation influences the apparent beneficial results.
U.S. Pat. No. 5,134,163 to Kingman proposes using topical applications of retinoic acid (tretinoin) to prevent and treat the lesions of striae distensae. A recent article (Elson, M. S., J. Dermatologic Surgery and Oncology, 16: 267-70 (1990)) reports improvements in the lesions of 15 of 16 patients treated with a topical tretinoin preparation. So it seems clear that topical application of active compounds can affect stretch marks. However, systemic retinoic acid absorption can result in birth defects and other undesirable side effects such as redness or dryness. Therefore, the material is available only under prescription.
U.S. Pat. No. 4,871,752 to Ilg et al. describes the use of aryloxycarboxylic acid derivatives as a treatment for stretch marks and various other dermatological conditions. These substances, however, are powerful drugs affecting lipid metabolism and seem to give the best results when applied topically together with ultrasound treatments.
U.S. Pat. No. 4,054,649 to Cariel describes the use of a topical solution containing extract of Alchemilla or Alchemilla with Hedera and/or Equisetum to ameliorate a number of dermatological disorders among which are stretch marks. Again, it is apparent from this work that plant extracts, as opposed to synthesized drugs, can also ameliorate stretch marks. However, Alchemilla is neither a commonly available nor commonly used herb in the United States at this time.
Keratoses due to photodamage or age may also show altered cellular constituents including weakened collagen fibers which are not inconsistent with stretch mark lesions. In fact, as mentioned above, there are patents employing retinoic acid to treat stretch marks. There has been considerable research aimed at treating photodamage to skin with retinoic acid.
It has now been discovered that a particular fraction of plant lipids, especially those from avocados or avocado seeds, are unexpectedly efficacious in treating both stretch marks and keratoses.